Programs used to write Math

What are some good programs to write math in? I do not like using microsoft word because it seems like a pain. Also I do not really want a program that solves what I write. I would just like a program to write math. Anybody know of one? Thanks, Matt

The one the pros use is LaTex. There are also freeware products, but they are a pain to set up and use (correct me if I'm wrong! If anyone knows of an easy to use workable freeware math text editor, please let us know).

There are also tools to convert .dvi files (which are LaTeX's raw output) to .png and other formats for inclusion on the web or in other kinds of documents. LaTeX has more than enough oomph to typeset entire books, however -- and it's a LOT more capable of flexible and less annoying than products like MS Word.